RANCID is Really Awesome New Cisco Config Differ. AS its name implies, RANCID monitors network device configuration, including software and hardware and uses CVS (Concurrent Version System) or Subversion to maintain history of changes. RANCID is simple and is easy to use.
The same very functionality of RANCID can be used as a backup system for Network device config backup system or even a config change alert system as it can email changes from previous saved configurations. All this RANCID does by logging on to a network device using Telnet or SSH and runs various show commands to grab config changes (hardware & Software), send alert emails of any changes, format the info and commit to the CVS system.
Some of the devices that RANCID supports
Cisco Routers and Cisco Catalyst Switches (IOS & CatOS)
HP ProCurve Switches
ADC EZT3 MUXs
MRTd & IRRd
RANCID is a Linux based software and needs to be compiled and installed (unfortunately there is no package built for specific Linux platforms)
RANCID can be downloaded from SHURBBERY networks here
RANCID requires the expect module installed on the Linux platform. A sample email notification showing changes based on the previous config versions can be found here.